Leigh syndrome is the most severe mitochondrial disease in children. It causes severe muscle weakness, movement defects, and intellectual disabilities. It usually leads to death within the first years of life. No causative treatment is currently available. One of the genes frequently mutated in patients is SURF1, which encodes for a protein involved in the process of energy generation in the cells. Animal models did not recapitulate the defects seen in the patients carrying mutations in SURF1. Therefore, the scientists did not have the tool to start understanding the disease mechanisms and to identify possible targets for treatment. They report about the first human model for this rare disease in Nature Communications, published on March 26th.